In the process of manufacturing an IC, a heat treatment apparatus is extensively used for heat treatment processes of forming a CVD (Chemical Vapor Deposition) film such as an insulating film, a metal film, a semiconductor film or the like on a wafer, or diffusing impurity into a wafer. Such a heat treatment apparatus includes a process chamber to process a plurality of wafers loaded in a boat (or a holder) in a batch mode, a waiting station in which the boat is waiting before or after being loaded or unloaded to/from the process chamber, a boat elevator provided in the waiting station to elevate the boat between the waiting station and the process chamber, a wafer transfer equipment provided in the waiting station to transfer the wafers to the boat, and a clean unit to supply clean air into the waiting station. In the heat treatment apparatus with this arrangement, the clean unit supplies nitrogen gas (used as inert gas) into the waiting station so that the nitrogen gas is circulated therein, which prevents a natural oxidation film from being formed on the wafer by oxygen (O2) in the atmosphere (see Japanese Patent Laid-Open Publication No. 2008-141176, for example).
In the heat treatment apparatus which circulates the nitrogen gas inside the waiting station, the nitrogen gas may be circulated from one side (typically from the front side) of the waiting station, so that a flow of the nitrogen gas in the waiting station may not be performed in a uniform manner. This may adversely affect the heat treatment. To address this problem, there is provided a mode in which the clean air from the clean unit is introduced into one side of the waiting station and is exhausted through an exhaust outlet formed in the other side (e.g., rear side) of the waiting station (hereinafter referred to as a “atmosphere mode”).
However, in the atmosphere mode-based heat treatment, the temperature of a portion of the clean air supplied from the clean unit is increased while it flows through the circulation path, which makes it difficult to evenly distribute the fresh clean air inside the waiting station.
In another approach, in order to suppress the generation of particles from the wafer and the wafer transfer equipment, or decrease the temperature in the periphery of the boat and the wafer transfer equipment, gas inlets formed in the circulation path are disposed in the vicinity of the boat and the wafer transfer equipment. However, even if such gas inlets of the circulation path are disposed in the vicinity of the boat and the wafer transfer equipment, it is difficult to suppress the generation of particles from the boat and the wafer transfer equipment while they are moving in a broad range. This may also result in a decrease of the wafer transfer speed.